Specimens of apocrine and eccrine sweat collected without and after pilocarpine stimulation from smokers and non-smokers exposed to tobacco smoke were investigated for the presence of nicotine. The concentrations were determined by radioimmunoassay, so that the values obtained represent the concentrations of nicotine plus its metabolites, e.g. cotinine. Measurable nicotine concentrations were found in all samples. The levels measured in apocrine sweat were higher than those in eccrine sweat. The presence of unchanged nicotine in sweat was revealed by GC/MS.